1. Field of the Invention
The present invention relates to a method of inspecting particles on wafers which can accurately inspect particles as real dust particles of foreign matters on wafers such as semiconductor wafers.
2. Description of the Related Art
Particles on wafers are originated from some foreign matters like dust particles or contaminants adhered thereon are to be severely controlled because the particles affect adversely a manufacturing process of semiconductor devices. A conventional control limit of particle size is about 0.3 .mu.m in diameter. As semiconductor devices become minuter, the particle size control limit of 0.2 .mu.m or 0.1 .mu.m or less is required. Particles on wafers are inspected by usually using a light scattering laser particle counter.
On the other hand, there exist a lot of crystal defects in silicon single crystals which are produced by usually using a CZ method. When wafers which are manufactured from silicon single crystals having a lot of crystal defects are treated by using a cleaning solution with etching effect such as a mixed solution of ammonia water, hydrogen peroxide water and water, the crystal defects are revealed predominantly as pits. If particles on the wafer are measured using a light scattering particle counter, the pits can not be discriminated from foreign matters like dust particles or contaminants because the pits act as light scattering points. Actually, with a light scattering particle counter, crystal defects of 0.2 .mu.m or less are counted as particles on wafers. The counted number goes usually up to 500-1000 pieces a wafer. There are 20-30 pieces of particles a wafer which is manufactured by a special method.
Moreover, it is known that epitaxial wafers have a limited number of crystal defects. There exist actually several crystal defects an epitaxial wafer. When particles on epitaxial wafers are inspected using a light scattering particle counter, the crystal defects are inspected as particles of about 0.1 .mu.m-0.2 .mu.m. In addition, there exist surface irregularities such as scratches generated by various causes. When particles on such wafers are inspected using a light scattering particle counter, the surface irregularities are inspected as particles of 0.2 .mu.m or less.
Thus, since crystal defects and surface irregularities such as scratches and particles of real dust particles or contaminants are confused in a particle inspection method using a light scattering laser particle counter, inspection of particles which are especially minute, for instance, 0.2 .mu.m or less could do nothing but become inaccurate.
Then, under the present circumstances, there is a great demand for a method of inspecting particles oil wafers which can accurately distinguish particles of 0.2 .mu.m or less from crystal defects or surface irregularities such as scratches.